Field of the Invention
The present invention relates to an objective lens for an endoscope and an endoscope. In particular, the present invention relates to an objective lens for an endoscope in which focusing is performed from a farthest point object to a nearest point object by moving a part of lens groups in a system, and also to an endoscope including this objective lens for an endoscope.
Description of the Related Art
In observation by endoscopes, users want to observe a wide range, as a whole, and also a part, such as a diseased region that has been found in observation of the whole area, in detail. Conventionally, such demand was often satisfied by using a fixed focus lens with a deep depth of field. However, further improvement in image qualities is requested, because the trend of endoscopes is a higher pixel number and a wider angle of view, and also because images imaged by endoscopes are read in and analysis and observation are performed on the images.
In view of such situations, objective lenses for endoscopes in which the usage state of an endoscope is switchable between a far-point-side observation state (wide), which is appropriate for observation of a region as a whole, and a near-point-side magnified observation state (tele), which is appropriate for observation of a part of the region, became used. As an example of such related art, an objective lens disclosed in Japanese Patent No. 2876252 (Patent Document 1) is known.
The objective lens for an endoscope disclosed in Patent Document 1 consists of four lens groups, and negative refractive power, positive refractive power, negative refractive power and positive refractive power are arranged in this order from an object side. Further, the usage state is switched, as described above, by moving a third lens group of the four lens groups.